1. Field of the Invention
The invention relates to an ink droplet ejecting method and apparatus of an ink jet type.
2. Description of Related Art
According to a known ink jet printer of an ink jet type, the volume of an ink flow path is changed by deformation of a piezoelectric ceramic material. When the ink flow path volume decreases, the ink present in the ink. flow path is ejected as a droplet from a nozzle. However, when the ink flow path volume increases, the ink is introduced into the ink flow path from an ink inlet. In this type of printing head, multiple ink chambers are formed by partition walls of a piezoelectric ceramic material. An ink supply device, such as ink cartridges, are connected to one end of each of the multiple ink chambers. The opposite end of each of the ink chambers is provided with an ink ejecting nozzle (hereinafter referred to simply as xe2x80x9cnozzlesxe2x80x9d). The partition walls are deformed in accordance with printing data to make the ink chambers smaller in volume, whereby ink droplets are ejected onto a printing medium from the nozzles to print, for example, a character or a figure.
An example of this type of ink jet printer is a drop-on-demand type ink jet printer that ejects ink droplets, which is popular because of a high ejection efficiency and a low running cost. An example of a drop-on-demand type ink jet printer is a shear mode type that uses a piezoelectric material, which is disclosed in Japanese Published Unexamined Patent Application No. Sho 63-247051.
As shown in FIGS. 7(a) and 7(b), this type of ink droplet ejecting apparatus 600 includes a bottom wall 601, a top wall 602 and shear mode actuator walls 603 (shown in FIG. 8 as 603a-g) located therebetween. The actuator walls 603 each include a lower wall 607 bonded to the bottom wall 601 and polarized in the direction of arrow 611, and an upper wall 605 formed of a piezoelectric material, the upper wall 605 being bonded to the top wall 602 and polarized in the direction of arrow 609. Adjacent actuator walls 603, as a pair, define ink chamber 613 (shown in FIG. 8 as 613a-d) therebetween. The actuator walls 603 that are adjacent to the ink chamber, in a pair, define a space 615 which is narrower than the ink chamber 613.
A nozzle plate 617 having nozzles 618 (shown in FIG. 8 as 618a-d) is fixed to one end of each of the ink chambers 613, while the opposite end of each of the ink chambers is connected to an ink supply source (not shown). Electrodes 619 (shown in FIG. 8 as 619a-d) and 621 are respectively formed on both side faces of each actuator wall 603, as metallized layers. More specifically, electrode 619 is formed on the actuator wall 603 on the side of the ink chamber 613, while electrode 621 is formed on the actuator wall 603 on the side of the space 615. The surface of electrode 619 is covered with an insulating layer 630 for insulation from ink. Electrode 621, which faces the space 615, is connected to a ground 623, and electrode 619, which is provided in each ink chamber 613, is connected to a controller 625, which provides an actuator drive signal to the electrode.
The one-way propagation time T is a time required for the pressure wave in the ink chamber 613 to propagate longitudinally through the same chamber. Given that the length of the ink chamber 613 is L and the velocity of sound in the ink present in the ink chamber 613 is a, the time T is determined to be T=L/a.
According to the theory of pressure wave propagation, upon lapse of time T, or an odd-multiple time thereof, after the above application of voltage, the internal pressure of the ink chamber 613 reverses into a positive pressure. In conformity with this timing, the voltage being applied to the electrode in the ink chamber 613c is returned to 0(V). As a result, the actuator walls 603e and 603f revert to their original state (FIGS. 7(a) and 7(b) before the deformation, whereby a pressure is applied to the ink. At this time, the above positive pressure, and the pressure developed by the reverting of the actuator walls 603e and 603f to their original state before the deformation, are added together to provide a relatively high pressure in the vicinity of the nozzle 618c in the ink chamber 613c, whereby an ink droplet is ejected from the nozzle 618c. An ink supply passage 626, shown in FIG. 7(b), that communicates with each of the ink chambers 613, is formed by members 627 and 628.
Conventionally, in this type of ink droplet ejecting apparatus 600, when an ink droplet of a small volume is to be ejected for enhancing the printing resolution, a control has been provided to decrease the driving voltage in multiple steps, for example. However, such a method of controlling the voltage in multiple steps leads to an increase in cost of a driver IC, etc., and attempting to reduce the volume of an ink droplet gives rise to the problem that even the speed of the ink droplet decreases. In order to obtain an ink droplet of a small volume without decreasing the ink droplet speed, it has been proposed to use an additional pulse of a low voltage level, after application of a jet pulse and before completion of ink ejection. However, this proposal also leads to an increase in cost of a driver IC, etc. because multiple voltages are needed as driving pulses.
The invention solves the above-mentioned problems, and it is an object of the invention to provide an ink droplet ejecting method and apparatus, wherein, after a driving waveform for a primary ejection of ink, only one additional pulse is added, thereby making it possible to obtain an ink droplet of a desired volume and also possible to minimize the decrease of the ink droplet speed.
In order to achieve this object, an ink droplet ejecting method is provided, wherein a jet pulse signal is applied to an actuator, for changing the volume of an ink chamber filled with ink, to generate a pressure wave within the ink chamber, thereby applying pressure to the ink and allowing a droplet of the ink to be ejected from a nozzle. Both the jet pulse signal and an additional pulse signal are applied to the actuator in accordance with a one-dot printing instruction. The jet pulse signal has a pulse width which allows the volume of the ink chamber to increase upon application of a voltage to the actuator, thereby causing a pressure wave to be generated within the ink chamber, and which, after the lapse of time T required for an approximately one-way propagation of the pressure wave through the ink chamber or after the lapse of an odd-multiple time of the time T, allows the volume of the ink chamber to decrease from the increased state to a normal state. The additional pulse signal has a pulse width of approximately 0.2T to 0.6T relative to the jet pulse signal, and a time difference between a fall timing of the jet pulse signal and a rise timing of the additional pulse signal is 0.3T to 0.7T.
According to the above method, the ink present in the ink chamber is about to rush out from the nozzle at the leading edge and the trailing edge of the jet pulse signal, and with the additional pulse signal which is subsequently applied halfway at the above timing, a part of the ink droplet which is rushing out from the nozzle is pulled back. Consequently, it is possible to reduce the size of the flying ink droplet after ejection, and hence possible to attain a high printing resolution easily. Further, since it is not necessary to change the driving voltage to reducing the size of the ink droplet, the cost is reduced and the ink droplet speed is only minimally decreased.
In accordance with another aspect of the ink droplet ejecting method, the jet pulse signal and the additional pulse signal have the same peak value. According to this method, a single drive voltage source is sufficient to obtain a small-sized ink droplet, and therefore the cost can be reduced.
An ink droplet ejecting apparatus is also provided that includes an ink chamber filled with ink, an actuator for changing the volume of the ink chamber, a driving power source for applying an electric signal to the actuator, and a controller which provides control so that, in accordance with a one-dot printing instruction, a jet pulse signal and an additional pulse signal are applied to the actuator from the driving power source, thereby causing the ink present in the ink chamber to be ejected. The controller provides control so that the jet pulse signal has a pulse width which allows the volume of the ink chamber to increase upon application of a voltage to the actuator, thereby causing a pressure wave to be generated within the ink chamber, and which, after the lapse of time T required for an approximately one-way propagation of the pressure wave through the ink chamber or after the lapse of an odd-multiple time of the time T, allows the volume of the ink chamber to decrease from the increased state to a normal state. The controller also provides control so that the additional pulse signal has a pulse width of approximately 0.2T to 0.6T relative to the jet pulse signal, and a time difference between a fall timing of the jet pulse signal and a rise timing of the additional pulse signal is 0.3T to 0.7T.
This structure provides the same advantages as the corresponding method in accordance with the invention discussed above.
In accordance with another aspect of this ink droplet ejecting apparatus, the jet pulse signal and the additional pulse signal have the same peak value. This structure provides the same advantages as the corresponding aspect of the method in accordance with the invention discussed above.
An ink droplet ejecting apparatus is also provided that includes an ink chamber filled with ink, an actuator for changing the volume of the ink chamber, a driving power source for applying an electric signal to the actuator, and a controller which provides control so that, in accordance with a one-dot printing instruction, a jet pulse signal for ejecting the ink present in the ink chamber and an additional pulse signal for withdrawing a part of an ink droplet which has rushed out from a nozzle in accordance with the jet pulse signal, are applied from the driving power source to the actuator. The controller determines whether or not the additional pulse signal is to be used. According to this apparatus, the volume of ink droplet can be adjusted by either applying, or not applying, the additional pulse signal in accordance with a preset resolution.
An ink droplet ejecting apparatus is also provided that includes an ink chamber filled with ink, an actuator for changing the volume of the ink chamber, a driving power source for applying an electric signal to the actuator, and a controller which provides control so that, in accordance with a one-dot printing instruction, a jet pulse signal for ejecting the ink present in the ink chamber and an additional pulse signal for withdrawing a part of an ink droplet which has rushed out from a nozzle in accordance with the jet pulse signal, are applied to the actuator from the driving power source. The controller provides control so that a time difference from the application of the jet pulse signal up to the application of the additional pulse signal, and the pulse width of the additional pulse signal, can be adjusted. According to this apparatus, since a control is provided so that the time difference from the application of the jet pulse signal up to the application of the additional pulse signal can be adjusted in accordance with a preset resolution, it is possible to adjust the volume of an ink droplet.
In accordance with another aspect of this ink droplet ejecting apparatus, the jet pulse signal has a pulse width which allows the volume of the ink chamber to increase upon application of a voltage to the actuator, thereby causing a pressure wave to be generated within the ink chamber, and which, after the lapse of time T required for an approximately one-way propagation of the pressure wave through the ink chamber or after the lapse of an odd-multiple time of the time T, allows the volume of the ink chamber to decrease from the increased state to a normal state. The pulse width of the additional pulse signal is controlled so as to be adjustable in the range of approximately 0.2T to 0.6T relative to the jet pulse signal, and the time difference is controlled so as to be adjustable in the range of approximately 0.3T to 0.7T from a trailing edge of the jet pulse signal up to a leading edge of the additional pulse signal. According to this apparatus, the decrease of the ink droplet speed is minimized, so that the same advantages can be attained as the ink droplet ejecting apparatus discussed above.
According to the invention, as set forth above, by adding a predetermined additional pulse signal to a jet pulse signal for a one-dot printing instruction, a small volume ink droplet can be provided at high speed, without decreasing the ink droplet speed. Further, since the volume of an ink droplet can be adjusted as desired, it is possible to obtain a desired printing resolution easily.
Further, unlike the conventional art, multiple driving voltages are not required to reduce the size of an ink droplet. One driving voltage source is sufficient, and it is not necessary to change the driving voltage, thus reducing the cost.